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POTASH FERTILISERS

135

B.    Determination of the Sodium Chloride

In a 500 c.c. flask 10 grams of the substance are boiled with about 250 c.c.
of water. If marked quantities of sulphate are present, 10% barium chloride
solution is now added, slowly and with shaking, until no further precipita-
tion occurs (excess is to be avoided) ; slight excess of baryta solution is then
added to the liquid and the latter boiled for about 15 minutes. With pro-
ducts free from or poor in sulphate, the baryta solution alone is added.
When cool, the solution is made up to the mark, mixed and filtered.

100 c.c. of the filtrate ( 2 grams of substance) are heated to boiling
in a 200 c.c. flask, ammonium carbonate solution being added gradually
and with shaking to the boiling liquid as long as any precipitate forms.
The solution is then heated (not boiled) until the precipitate becomes crystal-
line, and when cold made up to volume with recently boiled water, mixed
and filtered.

Of the filtrate, 100 c.c. (= I gram of substance) are evaporated to dry-
ness in a platinum dish and the residue gently heated to eliminate the, ammo-
nium salts, dissolved in a little hot water and filtered through a small filter.
The dish and filter are washed with hot water and the whole of the liquid
evaporated to dryness in a tared platinum dish, which is then dried in an
oven, heated gently at a dull red, and weighed.

The sodium and potassium chlorides corresponding with i gram of sub-
stance are obtained in this way. The amount of sodium chloride in the
mixed chlorides may be determined by two methods :

1.  The potassium is determined as platinichloride or perchlorate (see
p. 125).    K2PtCl, X 0-307 = KC1;   KC104 x 0-538 = KC1.    This method
is preferable when one of the two chlorides greatly predominates.

2.  The chlorine in the mixed chlorides is determined volumetrically (by
dissolving to a definite volume and titrating an aliquot part of the solution
with N/io-AgN03 according to Volhard's method), the quantity of NaCl
(x) being calculated, from the formula,

x = (p x 7-64632)  (P X 3-63354)'

in which p = grams of Cl in the mixed chlorides and P the weight of the pure
chlorides obtained from i gram of the substance.

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The strength (% K2O) of potassium salts is usually guaranteed as follows :

Kainit, minimum 12-4, but also 13, 13-5, 14, 14-5 and 15.

Carnallite, 9 ;   high quality carnallite, 13.

Sylvine, minimum 12-4, but also sold up to 16-20.

Hard salt, minimum 12-4.

Potassium chloride, minimum 56-8 for 90-95% KC1; 50-5 for 80-85% KCL

Potassium sulphate, 51-8 (96% K2SO4) and 48-6 (90% K2SO4).

Potassium and magnesium sulphate, 25-9.

Potash manure salts, 15, 20, 30, 38, 40, 42.

A certain importance as a fertiliser with a potash basis attaches to the
potash salt obtained by incinerating residues from the fermentation and distil-
lation of molasses. It consists mostly of potassium carbonate and its strength
(% of K20) is 45-49-5-entirely insoluble in hot water ; on ignition,